JP2018505839A - Polycrystalline cubic boron nitride (PcBN) containing microcrystalline cubic boron nitride (CBN) and fabrication method - Google Patents

Abstract

The polycrystalline cubic boron nitride compact includes a body having microcrystalline cubic boron nitride sintered in a matrix of binder material. Microcrystalline cubic boron nitride particles have a size in the range of 2 microns to 50 microns. The microcrystalline cubic boron nitride particles comprise a plurality of subgrains, each subgrain having a size ranging from 0.1 microns to 2 microns. The compact is produced by a high pressure-high temperature (HPHT) sintering method. The compact exhibits intergranular defect formation followed by the introduction of wear. Subgrains promote crack propagation based on micro-chipping rather than cleavage mechanism, and in sintered bodies, cracks propagate between grains rather than within grains, thereby toughening compared to single crystal cubic boron nitride And the wear characteristics are improved. The shaped body is suitable for use as an abrasive tool. [Selection] Figure 1B

Description

Related applications None

  The present disclosure relates generally to polycrystalline cubic boron nitride (PcBN). In particular, the present disclosure relates to preparing polycrystalline cubic boron nitride powder and a method of processing such polycrystalline cubic boron nitride powder into an abrasive tool. Polycrystalline cubic boron nitride powder exhibits a polycrystalline granular structure in which each of the polycrystalline cubic boron nitride particles contains a number of subgrains, and polishing made using such polycrystalline cubic boron nitride powder The tool preserves the polycrystalline granular structure.

  In the following description, reference will be made to specific structures and / or methods. However, the following references should not be construed as an admission that these structures and / or methods constitute prior art. Applicants expressly reserve the right to indicate that such structures and / or methods are not eligible for prior art to the present invention.

  Boron nitride cubic (cubic boron nitride (cBN)) is useful as an abrasive material. One such use is as a particle that aggregates using a bonding system to form an abrasive tool such as a grindstone. For applications as abrasive materials, particularly cutting tools, it is desirable for cubic boron nitride to contribute to wear, fraying and chipping properties, or at least not have a detrimental effect. Other applications include honing, dicing, and polishing.

  Machining requires that cutting tools have high wear characteristics, low fraying and chipping, and long life. Ideally, the failure mode of the tool is only wear, not any failure in the binder and / or cubic boron nitride feed induced by the propagation of microcracks or macrocracks. A conventional cubic boron nitride-based tool utilizes a single crystal cubic boron nitride powder in which each cubic boron nitride particle is a single crystal. The single crystal structure affects the failure mode of tools made from a single crystal cubic boron nitride feed, but it is not only that both microcracks and macrocracks are broken in the binder as well as single crystal cubic crystals. This is because it can also occur by cleavage of boron nitride crystals. Both of these fracture mechanisms contribute to reducing the performance of abrasive tools made from single crystal cubic boron nitride powder.

  Although sintering of cubic boron nitride involves the high pressure-high temperature (HPHT) method, technical improvements in the sintering of this type of material have mainly focused on the study of the binder phase. There is little research on the supply of boron nitride, and the cubic boron nitride powder in the supply affects the sintering and final performance of the sintered product, especially in machining applications.

  It would be beneficial in cubic boron nitride based abrasive tools to identify improvements in cubic boron nitride materials that contribute to improved wear performance and impact toughness.

  Cubic boron nitride can be synthesized as a microcrystalline mesh or micron particles consisting of multiple subgrains of micron or submicron (micrometer) size separated by grain boundaries, referred to as microcrystalline cubic boron nitride . See U.S. Pat. Nos. 2,947,617 and 5,985,228. The full texts of which are hereby incorporated by reference. Microcrystalline cubic boron nitride has an increased toughness than single crystal cubic boron nitride. Other advantageous properties of microcrystalline cubic boron nitride are: i) increased purity of cubic boron nitride particles free of residual metal catalyst and / or impurities; ii) higher toughness than standard single crystal cubic boron nitride powder Iii) crack propagation mode based on micro-chipping rather than cleavage mechanism; iv) in a sintered body, the crack propagates between particles rather than within the grains; and v) a massive crystal shape with rough surface properties obtain. Abrasive tools having a microstructure that includes polycrystalline cubic boron nitride particles include a number of subgrains separated by grain boundaries that impart improved wear performance and impact toughness.

  In one embodiment, the polycrystalline cubic boron nitride compact includes a body having microcrystalline cubic boron nitride sintered in a matrix of binder material. Microcrystalline cubic boron nitride particles have a size in the range of 2 microns to 50 microns. The microcrystalline cubic boron nitride particles comprise a plurality of subgrains, each subgrain having a size in the range of 0.1 microns to 2 microns.

  In another embodiment, a method for making a polycrystalline cubic boron nitride compact includes blending microcrystalline cubic boron nitride particles with a binder material under a controlled atmosphere to form a powder blend, and blending the high pressure-high temperature ( HPHT) collecting into a cell structure for use in the sintering process, and sintering the blend and applying high pressure and high temperature to the aggregate to form a polycrystalline cubic boron nitride compact. The polycrystalline cubic boron nitride compact includes a body comprising microcrystalline cubic boron nitride sintered in a matrix of binder material. Microcrystalline cubic boron nitride particles are particles having a size in the range of 2 microns to 50 microns. The microcrystalline cubic boron nitride particles comprise a plurality of subgrains, each subgrain having a size in the range of less than 0.1 microns to 2 microns.

  The foregoing summary, as well as the following detailed description, will be better understood when read in conjunction with the appended drawings. It should be understood that the illustrated embodiments are not limited to the precise configuration and instrumentalities shown.

A and B are scanning electron microscopy (SEM) photomicrographs of an exemplary embodiment of microcrystalline cubic boron nitride. A and B are scanning electron microscopy (SEM) micrographs of single crystal cubic boron nitride. A and B show exemplary shapes of supported and unsupported shaped bodies incorporating a sintered body of polycrystalline cubic boron nitride particles. It is a microscope picture of the scanning electron microscope (SEM) which shows the fine structure of the sample molded object produced using the microcrystal cubic boron nitride particle. It is a microscope picture of the scanning electron microscope (SEM) which shows the fine structure of the sample molded object produced using the single crystal cubic boron nitride particle. A and B are magnified photomicrographs of the scanning electron microscopy (SEM) of the microstructure shown in FIGS. 4A and 4B, respectively.

  1A and B are scanning electron microscopy (SEM) photomicrographs of an exemplary embodiment of polycrystalline cubic boron nitride. FIG. 1A shows a number of microcrystalline cubic boron nitride particles 10 magnified 2000 times. Microcrystalline cubic boron nitride particles have a D50 value of 18 micron particle size. The fluorescent X-rays (XRF) on the microcrystalline cubic boron nitride particles 10 are basically impurities of Co (8 ppm), Cr (10 ppm), Fe (69 ppm), Ni (25 ppm) and Si (19 ppm). It shows having a composition that is boron and nitrogen with levels. These impurities are derived from the grinding media introduced into the cubic boron nitride particles during the grinding process used to make such microcrystalline particles.

  Microcrystalline cubic boron nitride particles can be synthesized as mesh or micron particles composed of a plurality of subgrains of micron or submicron (micrometer) size and separated by grain boundaries. See U.S. Pat. Nos. 2,947,617 and 5,985,228. The full texts of which are hereby incorporated by reference.

  The microcrystalline cubic boron nitride particles 10 have a non-uniform shape and a very rough surface property. This surface property is a SEM micrograph of microcrystalline cubic boron nitride particles (specifically, microcrystalline cubic boron nitride particles 10 in the lower left corner of FIG. 1A) magnified 5000 times, more in FIG. 1B. Easily seen. In FIG. 1B, the microcrystalline cubic boron nitride particles 10 are uniform with non-linear edges and multiple height changes (both exhibiting a polycrystalline body (ie, a microcrystalline body)). Rather, there is an interlayer at the surface termination of the individual crystalline particles in the microcrystalline body. The height of the surface texture of each microcrystalline particle is determined by 1/2 the particle size of the subgrain exposed on the particle surface.

  Compared to microcrystalline cubic boron nitride particles 10, single crystalline cubic boron nitride particles were observed under scanning electron microscopy. 2A and 2B are scanning electron microscopy (SEM) photomicrographs of an exemplary embodiment of single crystal cubic boron nitride. FIG. 2A shows a number of microcrystalline cubic boron nitride particles 20 magnified 2500 times. Single crystal cubic boron nitride particles have a D50 value of 18 microns. The monocrystalline cubic boron nitride particles 20 have a smooth and faceted surface texture that indicates a direction that is crushed along the crystal plane of the monocrystalline structure. This surface texture is more easily seen in FIG. 2B, which is a SEM micrograph of single crystal cubic boron nitride particles 20 magnified 4000 times, indicating the layer formation of the crystal plane in region 25.

  Microcrystalline particles exhibit a massive shape with a very rough appearance and relatively non-straight crystal edges, while single crystal particles have a mixed appearance of roughness and smoothness and an angular shape with straight edges.

  The microcrystalline cubic boron nitride particles can be used as a feed to produce a sintered polycrystalline cubic boron nitride compact, or as a support or non-support compact. In an exemplary manufacturing process, microcrystalline cubic boron nitride particles are blended with a binder material under a controlled atmosphere, such as an inert atmosphere, to form a powder blend. The microcrystalline cubic boron nitride particle range can range in size from 1 micron to 50 microns, or 2 microns, 20 microns, or about 18 microns, the size being reported as the D50 value of particle size. The composition of the powder blend may contain 0 to 50 weight percent (wt%), alternatively 10 to 40 wt% binder. Suitable binder materials include Ti, Al and Zr nitrides, carbides, and carbonitrides such as TiN, TiC, Ti (C, N), ZrN, AlN, and Co and Al and mixtures thereof.

  The powder blend is then collected into a cell structure for use in high temperature-high pressure (HPHT) sintering methods known in the art. See U.S. Pat. No. 3,767,371. The full text of which is hereby incorporated by reference. As an example of the HPHT sintering method, the powder blend may be dispensed in contact with the surface of a substrate such as a hard sintered carbide disk. The powder-substrate combination is placed in a thin zirconium shield such as a container or metal wrapping that encapsulates the powder and optional substrate and excludes and removes oxygen. This assembly can then be surrounded one after another by high-pressure transmission elements, for example NaCl-based elements, to form HPHT cells. Multiple aggregates can be combined in an HPHT cell. The HPHT cell is then placed in an HPHT sintering apparatus, then high pressure and high temperature (5.5-7 Gpa, preferably 6 GPa, and 1,300 ° C. to 1,800 ° C., preferably 1,500 ° C.) for an appropriate time. Applied to sinter the powder blend and adhere the sintered powder blend to the surface of the optional substrate. Typical HPHT treatment times range from 30 minutes to 4 hours. After removing the pressure and allowing the HPHT cell to cool, the composite abrasive body can be recovered.

  An optional step in which the microcrystalline cubic boron nitride particles are pretreated can be included in the above manufacturing process prior to blending the microcrystalline cubic boron nitride particles with the blender material. The pretreatment step includes heating the microcrystalline cubic boron nitride particles in an ammonia atmosphere in a furnace at a temperature of 500 ° C. to 1,300 ° C., preferably 900 ° C. for 2 hours or less, preferably 1 to 2 hours. . The temperature and time can vary within these ranges in a shorter time when a high temperature is used and a longer time when a low temperature is used. The pre-treatment step cleans the surface of any contaminant microcrystalline cubic boron nitride particles. To help maintain the cleaned surface, the pretreated microcrystalline cubic boron nitride particles are stored and transferred to a subsequent manufacturing process in an inert gas environment. Further and as described above, the pretreated microcrystalline cubic boron nitride particles are blended with the binder material and the blending process also occurs under a controlled atmosphere such as performing the blending process in an inert gas.

  A composite abrasive including a substrate is known as a support molded body. The manufacturing process described above can also be performed in the absence of a substrate, in which case the recovered composite abrasive does not include a substrate. Such a composite abrasive body is known as an unsupported molded body. 3A and 3B show exemplary shapes of an unsupported molded body and a supported molded body 70, respectively. Support compact 70 includes a body 80 comprising microcrystalline cubic boron nitride sintered in a matrix of binder material. The main body 80 is coupled to the base material 90. The body 80 is integrally bonded to the substrate 90 by thermal diffusion of the metal phase in the substrate 90 to the contact surfaces of the sintered microcrystalline cubic boron nitride particles in the body 80. Unsupported shaped body 60 includes a body 62 comprising microcrystalline cubic boron nitride sintered in a matrix of binder material. In both the support molded body 70 and the non-support molded body 60, the sintered body includes a plurality of particles. Each of the plurality of particles has a plurality of subgrains. Each subgrain has a size ranging from less than 1 to 2 microns, or from 0.1 to 1.5 microns as measured by the MicroTrac particle characterization system. Typical microcrystalline cubic boron nitride particles having a particle diameter of 1 to 2 microns contain about 10 to about 5,000 subgrains, for example about 1000 subgrains.

  Microstructural investigations were performed on samples of unsupported compacts. One unsupported compact was made using microcrystalline cubic boron nitride particles as a feed for making via the HPHT process. The other support compact was used as a feed for producing single crystal cubic boron nitride particles via the HPHT process. The first sample (Sample A) is 6.75 grams of microcrystalline cubic boron nitride (cBN) particles having a D50 value of 18 micron particle size (available from Sandvik Hyperion as grade BMP 550 15-25). It was prepared by placing in a heat-resistant tube container. Two pieces of Al disk (0.012 ″ (0.3 mm) thick) were placed at both ends of the container and contacted with unbound cBN particles. Then, one of the graphite disks was in contact with the Al disk. By placing a graphite disk at each end of the heat-resistant tube container, the container was sealed, thereby forming a core assembly, which was then taken into the high pressure cell and the Ta disk and salt pressure permeable media pills. High pressure-high temperature (HPHT) sintering was carried out for a residence time of about 20 minutes at a pressure of 55 kbar and an immersion temperature of 1400 ° C. After the residence time, the cell was first Cooled for 4 minutes at a temperature drop rate of 0 ° C./min, then the total heating energy was terminated due to a rapid temperature drop using the coolant, the formed PcBN body of Sample A was a standard It had a quadrilateral of the tool shape.

For comparison, a second sample (Sample B) was prepared as a baseline and single crystal cubic boron nitride (cBN) particles having a particle size D50 of 18 micrometers (available from Sandvik Hyperion as grade CFB 180). Made using. The second sample was processed using the same HPHT processing conditions as Sample A. Sample A (invention) differs from Sample B (baseline) in the microstructure of the feed particles (ie, microcrystal vs. single crystal). Table 1 summarizes the details of the manufacturing process.

  Sample A is shown in FIG. 4A and sample B is shown in FIG. 4B. Both samples were prepared by crushing the sample to expose a cross section of the cubic boron nitride layer along the diameter of the generally cylindrical sample. Sample A (invention) and Sample B (baseline) were then further prepared for structural characterization using SEM with cross-section lapping and polishing followed by ion beam rolling as the final step.

  The microstructures of Samples A and B made according to the above details were investigated using scanning electron microscopy (SEM). The SEM device used was a Hitachi S4500, the settings were a voltage of 25 KV and a working distance of 12 mm. 4A is an SEM micrograph showing the microstructure of sample A, and FIG. 4B is an SEM micrograph showing the microstructure of sample B. FIG. Both FIGS. 4A and 4B are magnified 1000 times, and the bar gauge in FIG. 4A applies to FIG. 4B as well.

  The micrographs of FIGS. 4A and 4B show similar general sintering features. In both micrographs, coarse cubic boron nitride particles are separated by both fine cubic boron nitride particles (shown in black) and binder phase (shown in gray and white). In general, the size of the sintered particles in sample A is slightly smaller than the size of the sintered particles in sample B. Moreover, the sintered contact surface between the cBN particles of sample A and the binder phase (indicated by arrows labeled FIGS. 5A and 210) is that of sample B (labeled FIGS. 5B and 100). Coarser than indicated by arrows). In these photomicrographs, the roughness is determined by the surface properties of the sintered cBN particles. Microcracks in the sintered body were observed in both samples. These cracks are caused by crushing the sample with respect to the cross-sectional view, as seen in the arrow labeled 240 in FIG. 5A and the arrow labeled 110 in FIG. 5B.

  5A and 5B are magnified photomicrographs of the microstructure shown in FIGS. 4A and 4B and relate to Sample A and Sample B, respectively. These micrographs are magnified 5000 times and the sintered PcBN particles can be clearly distinguished, but there is a microstructural difference between sample A and sample B. First, the sintered particles in sample A (FIG. 5A) are more massive than the sintered particles in sample B (FIG. 5B). Second, the contrast of microcrystalline particles (subgrains) within each individual sintered particle in Sample A can be clearly observed as shown by the arrow labeled 250 in FIG. 5A. In addition, each microcrystalline particle also includes pits or voids on the surface, indicated by a circle labeled 230 in FIG. 5A. The size of the void or pit is in the nanometer range. These pits or voids mechanically improve the retention of cBN in the binder phase when cBN is processed into a polycrystalline body. In FIG. 5B, each of the single crystal cubic boron nitride particles in the photomicrograph is substantially uniform black with no change in contrast or contrast, so the sintered single crystal cubic boron nitride particles are Indicates that there is no subgrain. Third, in sample A (FIG. 5A), the contact surface between the microcrystalline cubic boron nitride particles and the binder is rougher than that of sample B (FIG. 5B). The relative increase in roughness between the microcrystalline cBN particles and the binder is due to the presence of the surface morphology of the microcrystalline cBN used for Sample A. In these micrographs, the roughness is determined to be about 1/2 of the cBN subgrain size.

  Finally, as indicated by the arrow labeled 240 in FIG. 5A, cracks were present in the binder phase in Sample A, which was caused by cross-sectional fracture during sample preparation. The cracks propagate between grains around individual microcrystalline cubic boron nitride particles, rather than within and through the grains of microcrystalline cubic boron nitride particles. The crack propagation path is indicated by an arrow 240 overlapping the micrograph. This intergranular crack propagation behavior is similar to the single crystal of sample B, where the cracks penetrated through the single crystalline cubic boron nitride particles and broke the single crystalline cubic boron nitride particles, i.e., the cracks propagated within the grains. Different from that observed with crystalline cubic boron nitride. Considering the fact that Sample A containing microcrystalline cBN sample particles is coarser than Sample B containing single crystalline cBN particles, the microcrystalline particles can absorb crack energy and / or deviate from the crack propagation path. Indicates the ability to terminate crack propagation.

Compositions with microstructure features of sintered polycrystalline cubic boron nitride bodies of Sample A and Sample B were analyzed using EDX. The areas of microstructure that were investigated are shown in FIG. 5 and include: The gray area (300) was identified by aluminum diboride (AlB ₂ ). A bright area (310) near AlB ₂ was identified as aluminum boride (AlN). AlB ₂ and the region between the AlN (320) is a cBN phase. Region 330 is an island-like domain within the AlB ₂ region that was also investigated and identified as a cBN crystal (see Spectrum 4). Based on color contrast, SEM micrographs qualitatively show that there are more AlB ₂ phases in the binder than AlN phases in both Sample A and Sample B. Table 1 summarizes the EDX results for these four regions including the amount of components (atomic percent (at.%)) And identification of the composition of the region.

  Although specific embodiments are mentioned, it is obvious that other embodiments and variations can be devised by those skilled in the art without departing from the spirit and scope thereof. It is intended that the appended claims be construed to include all such embodiments and equivalent variations.

Claims (15)

A polycrystalline cubic boron nitride compact comprising a body comprising microcrystalline cubic boron nitride sintered in a matrix of binder material:
The microcrystalline cubic boron nitride is a particle having a size ranging from 2 microns to 50 microns;
The microcrystalline cubic boron nitride particles comprise a plurality of subgrains, each subgrain having a size ranging from 0.1 microns to 2 microns;
Polycrystalline cubic boron nitride molded body.   The polycrystalline cubic boron nitride molded body according to claim 1, further comprising a base material, wherein the main body is integrally bonded to the base material.   The polycrystalline cubic boron nitride compact according to claim 1 or 2, wherein each subgrain has a size in the range of 0.5 microns to 1.5 microns.   3. The polycrystalline cubic boron nitride compact according to claim 1 or 2, wherein the microcrystalline cubic boron nitride particles contain from about 10 to about 5000 subgrains.   3. The polycrystalline cubic boron nitride compact according to claim 1 or 2, wherein the composition of the main body comprises up to 50% by weight of a binder material.   The polycrystalline cubic boron nitride compact according to claim 5, wherein the binder material is selected from the group consisting of Ti, Al, Zr, Co, Al nitrides, carbides, carbonitrides, and mixtures thereof. .   3. The polycrystalline cubic boron nitride compact according to claim 1, comprising microcrystalline cBN particles having surface properties approximately half the size of as-grown surface voids or pits and subgrains. A method for producing a polycrystalline cubic boron nitride compact comprising:
Blending microcrystalline cubic boron nitride particles with a binder material under a controlled atmosphere to form a powder blend;
Collecting the blend into a cell structure for use in a high pressure-high temperature (HPHT) sintering process;
Sintering the blend and forming a polycrystalline cubic boron nitride compact by applying high pressure and high temperature to the assembly,
A polycrystalline cubic boron nitride compact comprises a body comprising microcrystalline cubic boron nitride sintered in a matrix of binder material;
The microcrystalline cubic boron nitride is a particle having a size in the range of 1 to 50 microns;
The microcrystalline cubic boron nitride particles comprise a plurality of subgrains, each subgrain having a size in the range of less than 0.1 microns to 2 microns;
Method.   9. The method of claim 8, wherein the cellular structure includes a substrate having a surface in contact with the blend, and the polycrystalline cubic boron nitride compact includes a substrate and a body integrally bonded to the substrate. .   Further comprising heating the microcrystalline cubic boron nitride particles to a temperature in the range of 500 ° C. to 1,300 ° C. for up to 2 hours in an ammonia atmosphere before blending the microcrystalline cubic boron nitride particles with the binder material; 10. A method according to claim 8 or 9.   10. A method according to claim 8 or 9, wherein each subgrain has a size in the range of 0.5 microns to 1.5 microns.   10. The method of claim 8 or 9, wherein the microcrystalline cubic boron nitride particles contain about 10 to about 5000 subgrains.   10. A method according to claim 8 or 9, wherein the composition of the body comprises up to 50% by weight binder material.   14. The method of claim 13, wherein the binder material is selected from the group consisting of Ti, Al, Zr, Co, Al nitrides, carbides, and carbonitrides, and mixtures thereof.   10. The method according to claim 8 or 9, wherein the polycrystalline cubic boron nitride compact contains microcrystalline cBN particles having a surface texture that is approximately half the size of the as-grown surface voids or pits and subgrains.

Images